1. Field of the Invention
This invention relates to vibration controllers and methods for reducing of vibrations on stationary components of rotary machinery such as turbines, generators, pumps, motors, fans, and the like. In particular, the invention relates to such controllers and methods which provide an active dynamic controlled damping of vibrations through the use of a magnetic coupling.
2. Description of the Prior Art
For over three quarters of a century, dynamic vibration controllers have been known and used to eliminate resonances which occur in structures when a rotary machine is operated in a steady state condition at a particular rotational frequency. The approaches applied to date for dynamic vibration controllers are mechanical spring-mass damper systems that are tuned so that the natural frequency of the damper is the same as the frequency of the unbalanced force acting on the structure being subjected to vibration control. The dynamic vibration controller generates a force that is equal and opposite to the main system driving force, thereby resulting in a balancing of forces and negligible vibration of the main system. However, the characteristics of the known dynamic vibration controllers are limited in their range of application due to the fact that the spring constants and masses are fixed at the time of design, and while the controllers are tuneable at the time of installation, such as by adjustments to the damper mass, they do not possess the ability to change stiffness and damping characteristics during operation in order to compensate for system resonances during transient machinery operation (such as speed changes).
On the other hand, many machines experience resonance conditions during variable speed operation and some even under steady state conditions. Vibration resonances which occur during transient machinery operations as well as those that occur during steady state operation are undesirable due to the direct effects of the vibrations on the machinery and due to the noise generation associated therewith. Thus, there is a need for an active dynamic vibration controller that will have the ability to provide a controllable damper natural frequency that will allow the damper to compensate for system resonance during transient machinery operation and under various steady state operating conditions, i.e., that can reduce single or multiple vibration resonances.